Field of the Invention
The present invention relates to a method for operating a contactless ultrasound or radar fill level measuring device having at least one open distribution transmitter, at least one receiver and at least one evaluation unit comprising the following steps: emitting a transmitter signal by the transmitter, receiving a reflection signal reflected on a reflector by the receiver, evaluating the transmitter signal and/or the reflection signal by the evaluation unit. Furthermore, the invention relates to a contactless ultrasound or radar fill level measuring device comprising at least one open distribution transmitter for emitting a transmitter signal, at least one receiver for receiving a reflection signal reflected on a reflector and at least one evaluation unit designed for evaluating the transmitter signal and/or the reflection signal.
Description of Related Art
Contactless fill level measuring devices for the measurement of the fill level of a fill product arranged in a container as well as methods for operating this device are known from the prior art. A known measuring principle, which forms the basis for the determination of the fill level, is the transit time method. Thereby, during a measurement cycle, an ultrasound or radar signal is emitted from a transmitter in the direction of the fill product and, after being reflected on the surface of the fill product, is received by a receiver as a reflection signal. The transit time of the reflection signal is dependent on the traversed path. In this respect, the distance to the fill product can be determined from the transit time and, from it, the fill level in the container.
A problem that this measuring principle has, is that the transmitter signal is not reflected solely on the fill product surface, but also on so-called static interrupters such as container installations, welding seams or the floor of the container. A reflection signal detected by the receiver is, consequently, a superimposition of individual reflections on different reflectors. The individual reflection signals can be differentiated based on their differing transit times. By recording the reflection signal of an empty container, in particular, it is possible to filter out the portions that are caused by reflections on static interrupters from the reflection signal during fill level measurement.
In addition to static interrupters, however, dynamic interference sources can also influence the measuring process.
Dynamic interferences occur, for example, when the fill product passes through the transmitter signal during the filling event of the container. Namely, it is possible that the transmitter signal at least partially passes through the in-flowing medium, but a reliable measurement of the medium is not given. In order to ensure a reliable fill level measurement, dynamic interferences also have to be taken into account in evaluating the reflection signal.
Currently, dynamic interferences in fill level measurement are taken into account in that the identified measured fill level is subjected to a plausibility check before it is output. For this, for example, a window is determined based on the current fill level, depending on the expected change of the fill level, within which measured fill levels are plausible. If a determined measured fill level is located outside of this window, it is rejected as being implausible.
The German Patent Application DE 10 2013 103 532 A1 and corresponding US Patent Application Publication 2016/047684 disclose a method for measuring the fill level of a fill product in a container, wherein a plausibility check is carried out based on historical and current measurement points and, based on the plausibility check, historical and/or current measurement points deemed implausible are deleted. A further evaluation of the deleted measured values does not take place. In particular, there is no assignment of the measured values deemed implausible to a corresponding interference source.
A disadvantage of this method is that, on the one hand, there is no assignment of the error signal to an interference source, so that elimination and/or consideration of the interference is not possible when outputting the fill level. On the other hand, a filling stream having a small distance to the fill product surface and, in particular, being within the plausibility window is not acknowledged as a measuring error.
Based on this prior art, the object of the present invention is to provide a method for operating a contactless ultrasound or radar fill level measuring device and to provide a contactless ultrasound or radar fill level measuring device, which provides a particularly high reliability of fill level measurement.